Apparatus for the optical manipulation of a pair of landscape stereoscopic images

ABSTRACT

Apparatus ( 2 ) for the optical manipulation of a pair of landscape stereoscopic images, which apparatus ( 2 ) comprises a housing ( 4 ), and optical re-orientation means ( 6 ) positioned in the housing ( 4 ) and for re-orienting the pair of landscape stereoscopic images between a first orientation required for human viewing and a second orientation required for recording with a single camera or for reproduction from a single screen.

[0001] This invention relates to apparatus for the optical manipulationof a pair of landscape stereoscopic images.

[0002] Normal human eye sight is stereoscopic. This means that the humanbrain is able to judge the distance to an object by comparingdifferences between the images captured by each eye from differentpositions. Eye separation is typically 63 mm but the ability tointerpret relative distances is still maintained when this image captureseparation distance is artificially increased, for example as withbinoculars, or is artificially reduced, for example as with a microscopeor an endoscope.

[0003] Stereoscopic images have been captured historically by the use oftwo cameras and complex means for directing the resulting imagesseparately to each eye. In some cases, separate but linked projectorshave been used together with polarising spectacles in order to segregatethe images superimposed on a screen. A variation on this, usuallyemployed for video purposes, is to show left and right imagesalternately to the same camera. The images alternate in time and/or asstrips across a screen, either horizontally or vertically. All of theseknown systems have an adverse affect on image quality, unless additionalcomplications are included by way of memory to fill in the gaps for eachof the stereoscopic images. Such additional complications requirededicated and complicated electronics, which must also direct theassembled components of each image to the appropriate human eye.

[0004] A passive optical system is known from United Kingdom Patent No.2,236,198. In this patent, landscape shaped images from separate lensesare reorientated such that each image fills half the area of view of asingle camera simultaneously, and without the images having theirproportions compressed along one axis. Essentially, the images arerotated 90° anti-clockwise in their own plane and shown to a singlecamera with their longest sides adjoining. When displayed on atelevision or monitor screen, this means that every scan line, field andframe contributes to both images. In most electronic stereoscopicviewing systems, this is not true. A television screen is normallyscanned on alternate lines (field 1) followed by the in-between lines(field 2), and many electronic stereoscopic viewing systems devote onefield to the left eye and the other field to the right eye. These knownelectronic stereoscopic viewing systems are described as fieldsequential viewing systems. Flicker is a known complication as theimages alternate when displayed to each eye in turn. Two consecutivefields on monoscopic television make up a whole frame.

[0005] Passive optical viewing apparatus is disclosed in United KingdomPatent No. 2,283,877. Whilst this is a considerable improvement on manyknown types of stereoscopic viewing apparatus, the apparatus of theUnited Kingdom Patent No. 2,283,877 has its images rotated through 90°which require images viewed, for example, on a television, to be suchthat the television has to be rotated through 90°. This can beinconvenient.

[0006] It is an aim of the present invention to obviate or reduce theabove mentioned problem.

[0007] Accordingly, in one non-limiting embodiment of the presentinvention there is provided apparatus for the optical manipulation of apair of landscape stereoscopic images, which apparatus comprises ahousing, and optical re-orientation means positioned in the housing andfor re-orientating the pair of landscape stereoscopic images between afirst orientation required for human viewing and a second orientationrequired for recording with a single camera or for reproduction from asingle screen, the single screen being such that it has a first pair ofsides which are shorter than a second pair of sides, the secondorientation being such that there is no top to bottom inversion of oneof the landscape stereoscopic images with respect to the other one ofthe landscape stereoscopic images, the second orientation being suchthat the stereoscopic landscape images are rotated for display in eachof two halves of the single screen such that the longest sides of thestereoscopic landscape images are parallel with the first pair of sidesof the screen thereby maintaining a good aspect ratio without the needfor compression or stretching of the pair of landscape stereoscopicimages, and the optical re-orientation means being such that the pair oflandscape stereoscopic images leave the optical re-orientation means ina direction which is parallel to a direction in which the pair oflandscape stereoscopic images enter the optical re-orientation means.

[0008] The apparatus of the present invention is such that images can beviewed without having to rotate the image source through 90 °.

[0009] The apparatus of the present invention may include a firstoptical path for conveying a first one of the pair of landscapestereoscopic images, and a second optical path for conveying a secondone of the pair of landscape stereoscopic images.

[0010] The apparatus of the present invention may be one in which theoptical re-orientation means re-orientates one of the pair of landscapestereoscopic images such that the landscape stereoscopic images are sideby side in landscape format at a first end of the first and the secondoptical paths, such that the landscape stereoscopic images are on top ofone another at a second end of the first and the second optical paths,and such that the landscape stereoscopic images are the same way up atthe first and the second ends of the first and the second optical paths.The optical paths may be any suitable and appropriate optical pathsincluding relay lens optical paths and fibre optic optical paths.

[0011] Preferably, the optical re-orientation means comprises fourreflective surfaces. This enables two lateral inversions of each imagebetween the display device and the eyes unless one of the images is seendirectly. One of the two lateral inversions may be by electrical means.

[0012] The apparatus may be one in which the optical re-orientationmeans comprises a first one of the reflective surfaces for reflectingone of the landscape stereoscopic images upwardly, a second one of thereflective surfaces for reflecting the image from the first reflectivesurface towards the second end of the first and the second opticalpaths, a third reflective surface for reflecting the image from thesecond reflective surface towards and above the one of the landscapestereoscopic images that has not been re-orientated, and a fourthreflective surface for reflecting the image from the third reflectivesurface towards the second end of the first and the second optical pathsand parallel with and above the one of the landscape stereoscopic imagesthat has not been re-orientated.

[0013] Preferably, the four reflective surfaces are four prism surfaces.Other types of reflective surfaces may be employed so that, for example,the reflective surfaces may be parts of mirrors.

[0014] In an alternative embodiment of the invention, the opticalre-orientation means may include three reflective surfaces off which atleast one of the landscape stereoscopic images is sequentiallyreflected, and electrical image-reversal means for providing a screenoutput as a mirror image. If desired, the apparatus may include flatpanel display means, and in which the steroscopic pair of images from aflat panel display on the flat panel display means are able to besuperimposed and segregated by passive polarising spectacles, despitethe display panel having inbuilt polarisation opposite to that requiredfor one of the two images.

[0015] In a further embodiment of the invention, the polarising filtersmay be omitted from the display screen, and a lenticular overlay usedinstead in order to cover a matrix of optical fibres where the lightemerges. This is to enable stereoscopic viewing by means of angularseparation of the images, without the use of spectacles. In order toexploit the lenticular overlay, vertical strips of each image alternateacross the fibre optic matrix. The same arrangement may be used for usewith polarising spectacles, which do not provide the same restrictionson viewing position, but in this case light has to be polarised for theimages in opposite senses.

[0016] The apparatus for the present invention may find application in awide variety of fields including medical fields, industrial fields, andmedia fields. Thus, the apparatus of the present invention may beproduced in the form of a stereoscopic endoscope, a professional videoset-up and home stereoscopic recording system, in pick-and-placemanufacturing systems, in ophthalmic apparatus, and in live cameraprojection apparatus. The apparatus of the present invention iscompatible with television systems broadcasting using a singleunmodified analogue or digital video channel. The apparatus of thepresent invention is also compatible with the internet.

[0017] As mentioned above, one example of an industrial application ofthe apparatus of the present invention is that of an endoscope.Endoscopes are widely used by surgeons. The surgeons frequently operatethrough minimum size apertures in order to speed the healing process ofa patient, in what is often called keyhole surgery. In order to do this,the surgeons need to see inside the patient's body. Tubular instrumentswhich can bring out such images are called endoscopes. The knownendoscopes may be rigid or flexible depending upon their intended use.The known endoscopes may have a diameter of only a few millimetres. Acamera may operate from inside the endoscope, or an image may beconveyed along the endoscope by optical means from inside the patient toa camera head controlled directly by the surgeon. Results may be viewedon a monitor screen. The known endoscopes give monoscopic images whichdo not allow a surgeon the benefit of depth and distance perceptionsince both eyes receive the same image. Many attempts have been made tobring stereoscopic views to the surgeon by following the above mentionedelectronic image switching principles. These attempts have given rise toa common problem in that the images alternate in various ways and soonbecome tiring. With the apparatus of the present invention in the formof an endoscope, stereoscopic images are able to be conveyed along theendoscope by two optical paths and they are able to be re-orientated,for presentation to a single camera simultaneously. On a conventionaldisplay tube, every line, field and frame contributes to both images.

[0018] The two optical channels may be in the form of rod lenses insidea tube where positive and negative lenses share the same focus. Repeatpairs in series along the length of a rigid endoscope may maintain thesize of the image, each in a similar fashion to a telescope. The twooptical paths may alternatively comprise two coherent bundles of opticalfibres which are flexible. Pin prick samples of an image from inside apatient may be kept in the same relative positions as they are conveyedto the other end of the endoscope arriving in the manner of pixels onthe face of a display screen.

[0019] In either a rigid or flexible endoscope in accordance with thepresent invention, the images are shown one above the other (instead ofside by side) to a single camera which is rotated 90° clockwise in orderto capture the combined shape of the two images. Once captured by thecamera, the images may be conveyed to a single monitor, television orprojector. The apparatus of the present invention in the form of anendoscope is advantageous over known endoscopes insofar as it providesseparate stereoscopic images from two optical channels which are shownto a single camera simultaneously, each occupying half the area of view,such that on a conventional television or monitor tube every line, fieldand frame contributes to both images. Most alternative viewing systemsare based on field sequential viewing as mentioned above so that theimages in whole or in part alternate. Memory storage and othercomplications are necessary in order to reduce the effects of flicker.

[0020] In its endoscope form, the apparatus of the present invention maybe used with analogue, digital or film systems. A surgeon or other userdoes not require a completely new set of equipment. A known monoscopicendoscope may be replaced by a stereoscopic one in accordance with thepresent invention on the same medically approved camera. The addition ofpassive optical re-orientation of the medical monitor screen output thenpermits the surgeon to view stereoscopically through passive polarisingspectacles which segregate the superimposed images. The endoscope usermay still see normally when looking away from the screen. Electronicallyswitched viewing systems interfere with normal vision. For example theremay be a beat frequency with the mains lighting.

[0021] A monitor without a stereoscopic viewer attachment will displayphysically separate images. Electronic stereoscopic displays show anunwatchable mixture of images if the viewing segregation mechanism isabsent.

[0022] Embodiments of the invention will now be described solely by wayof example and with reference to the accompanying drawings in which:

[0023]FIG. 1 shows first apparatus of the invention for the opticalmanipulation of a pair of landscape stereoscopic images;

[0024]FIG. 2 shows second apparatus of the invention for the opticalmanipulation of a pair of landscape stereoscopic images;

[0025]FIG. 3 shows third apparatus of the invention for the opticalmanipulation of a pair of landscape stereoscopic images;

[0026]FIG. 4 shows a fourth apparatus of the invention for the opticalmanipulation of a pair of landscape stereoscopic images;

[0027]FIG. 5 shows fifth apparatus of the invention and more especiallyshows an example of optical re-orientation of a pair of screened imagesby means of optical fibres, enabling image segregation by either anangular displacement overlay matrix or polarisation filters;

[0028]FIG. 6 shows how a television or monitor display can be viewedthrough polarising spectacles or a lenticular overlay, and should beconsidered in relation to FIG. 5;

[0029]FIG. 7 shows part of sixth apparatus of the invention for theoptical manipulation of a pair of landscape stereoscopic images, and isin principle a component part of FIG. 2; and

[0030]FIG. 8 is a side sectional view of the apparatus shown in FIG. 7.

[0031] Referring to FIG. 1, there is shown apparatus for the opticalmanipulation of a pair of landscape stereoscopic images. The apparatus 2comprises a housing 4 which is shown in exploded form for ease ofunderstanding. The apparatus 2 also comprises optical re-orientationmeans 6 which is positioned in the housing 4 and which is forre-re-orientating the pair of landscape stereoscopic images between afirst orientation required for human viewing and a second orientationrequired for recording with a single camera or for reproduction from asingle screen, the single screen being such that it has a first pair ofsides which are shorter than a second pair of sides. The secondre-orientation is also such that there is no top to bottom inversion ofone of the landscape stereoscopic images with respect to the other oneof the landscape stereoscopic images. The second orientation is furthersuch that the stereoscopic landscape images can be rotated for displayin each of two halves of the single screen such that the longest sidesof the stereoscopic landscape images are parallel with the first pair ofsides of the screen, thereby maintaining a good aspect ratio without theneed for compression or stretching of the pair of landscape stereoscopicimages.

[0032] The optical re-orientation means 6 is further such that the pairof landscape stereoscopic images leave the optical re-orientation means6 in a direction which is parallel to a direction in which the pair oflandscape stereoscopic images enter the optical re-orientation means 6.

[0033] As can be seen from FIG. 1, the optical re-orientation means 6comprises two mirrors 8, 10 which just reflect light, and a mirror 12which both reflects and transmits light. The mirror 12 is a halfsilvered mirror which reflects substantially 50% of the light and whichtransmits substantially 50% of the light. The optical re-orientationmeans 6 further includes polarising filters in a polarising frame 14 andpolarising spectacles 16. The mirror 12 may have a metal ormetallic-type material other than silver for giving the 50% reflectionand the 50% transmission of the light.

[0034] As can be seen from FIG. 1, images are viewed via the polarisingspectacles 16 from a television 18 having a base 20, a top 22 and sides24, 26. The television 18 is thus standing in a normal upright mannerwith its screen facing the housing 4.

[0035] The mirror 12 is positioned between the mirror 8 and the mirror10. A first polarising filter 28 is positioned in the polarising frame14 such that it is between the television screen and the mirror 8. Asecond and contrastingly polarised filter 30 is positioned in thepolarising frame 14 such that it is between the television screen andthe mirror 12. A third polarising filter may advantageously be includedwhich is perpendicular to the first and second filters and whose planepasses through their dividing line. This third filter device may benecessary where a screen is already polarised across its whole area. Inthis case a 90° phase shift becomes necessary for the left eye image,achieved for example by passing it through a circular polariser followedby a linear one.

[0036] The mirror 8 is hinged about an edge 32, allowing the viewingapparatus to adapt for a smaller screen size. The mirror 12 makes anangle of 45° as shown.

[0037] Referring now to FIG. 2, there is shown second apparatus 42 whichis similar to the apparatus 2 shown in FIG. 1. Similar parts have beengiven the same numerals for ease of comparison and understanding. Theapparatus 42 is slightly more compact than the apparatus 2.

[0038] In both the apparatus 2 and the apparatus 42, it will beappreciated that the light path of the original image has been folded toavoid the need for rotating the display screen.

[0039] In both the apparatus 2 and 42, the upper mirror 10 mayadvantageously be hinged about its upper edge. Slight adjustment of itsnormal 45° angle then facilitates viewing from a variable verticalposition.

[0040] A vertical swivel axis through the centre of the mirror 10 andthe mirror beneath it may facilitate directing the stereoscopic viewhorizontally.

[0041] The viewing surface of the mirror 10 enclosure may usefully be asheet of anti-reflection coated glass or coated plastic (not shown).This provides some mechanical protection for the optics, excludes dust,and reduces spurious reflections from external light sources.

[0042] Referring now to FIG. 3, there is shown third apparatus 52 forthe optical manipulation of a pair of landscape stereoscopic images. Theapparatus 52 comprises a housing 54 which is shown in exploded form forease of understanding. The housing 54 contains mirrors 56, 58, 60 and62. The mirrors 56, 60 are both mounted with their reflecting surfacesangled downwardly. The mirrors 58 and 62 are both mounted with theirfull reflecting surfaces angled upwardly. The mirror 56 may be rotatableabout its upper edge 64 to enable stereoscopic viewing of a smallerpicture display panel.

[0043] The mirror 62 may be rotated about a horizontal axis CD or,alternatively, its enclosure distance from a right eye arrangement 66may be changed to facilitate a human brain merging the images from theright eye arrangement 66 and a left eye arrangement 68 for eyeseparations which differ. The axis CD may coincide with upper or lowerhorizontal mirror edges, or be intermediate.

[0044] The apparatus 52 is shown in exploded form for clarity. Inpractice, the apparatus 52, as with the apparatus 2 and 42, needs toexclude light from entering the eyes from anywhere but the appropriatepart of the apparatus, in common with monoscopic use of a view finder.The optical re-orientation means need to be enclosed, usually with theappropriate use of eye cups. Internal non-reflective surfaces may bematt black. A vertical partition of the images may be essentially opaqueand it may extend to the height and width of the mirror 60.

[0045] As can be seen from the lower part of FIG. 3, the pair oflandscape stereoscopic images are marked L,R and, they are provided on ascreen 70 with a two-axes swivel mounting 72 by a camcorder (remaindernot shown). The camera display screen is able to show such a pair ofimages by means of an optical manipulation camera attachment to the lensdescribed in United Kingdom Patent No. 2,236,198. As can also be seenfrom FIG. 3, the images L,R are able to be seen one above the other,with the apparatus 52 enabling each image L,R to be directed separatelyto the appropriate eye, at the right eye arrangement 66 and the left eyearrangement 68, this being in the manner of looking downwards into apair of binoculars.

[0046] The apparatus 52 offers the choice of viewing with or withoutpolarising glasses 16. Glasses are no advantage in this case.

[0047] The apparatus may be used with 180° rotation in principle, sothat the eye pieces become swopped over. The right eye image would bedirectly beneath the left eyepiece, instead of the left eye image on thescreen being below the right eye-piece as shown in FIG. 3.

[0048] Referring now to FIG. 4, there is shown apparatus 82 for theoptical manipulation of a pair of landscape stereoscopic images. Theapparatus 82 is in the form of an endoscope.

[0049] The apparatus 82 comprises an optical channel positive lenselement 84 for the left eye view, and an optical channel positiveelement 86 for the right eye view. There is also an optical channelnegative lens element 88 for the right eye view. A patient's body isshown schematically as body surface 90 and it will be seen that theright hand end of the apparatus 82 is in the patient, whilst the lefthand end of the apparatus 82 is outside the patient.

[0050] The apparatus 82 further comprises a prism reflective surface 92for the right eye view. This prism reflective surface 92 gives a firstreflection which is upwards.

[0051] The apparatus 82 further comprises a prism reflective surface 94for the right eye view. This prism reflective surface 94 gives a secondreflection which is directed towards the surgeon. A prism reflectivesurface 96 for the right eye view gives a third reflection which isdirected across and towards the left eye view optical axis, but aboveit. A prism reflective surface 100 for the right eye view provides afourth reflection which is directed parallel to the left eye viewchannel, but directly above it.

[0052] The same re-orientation of the two images could be achieved byusing a coherent bundle of optical fibres to relocate the right eyeimage above that of the left eye. Pin prick samples of an image arepreserved in the same relative positions, in the manner of pixels on ascreen, when a coherent bundle of fibres relocates an image. The fibrebundle “S” shape would replace the four reflective surfaces.

[0053] Also shown in FIG. 4 are a positive lens element 102 at thecamera end of the right eye view channel, and a positive lens element104 at the camera end of the left eye view channel. A common focus 11 isshared by the relay elements 86, 88. The magnification is given by theratio of the focal lengths.

[0054] The right eye view 106 and the left eye view 108 are capturedsimultaneously by a single camera.

[0055] The reference numeral 110 is shown as a discontinuous line in theleft eye view purely for clarity. The left eye channel is in principle astraight monoscopic endoscope.

[0056] The reference numeral 112 indicates a right eye view from thebottom patient end of the apparatus 82. The reference numeral 114illustrates the left eye view from the bottom patient end of theapparatus 82. A common target 116 is shown being viewed by both the leftand right eyes. The optical axes are made to converge on the commontarget 116.

[0057] Optical relays in the form of pairs of lenses are represented atboth ends of the right eye channel to illustrate the principle. Inreality, the optical relays may consist of standard endoscope rod lenseswhich repeat along the length of the endoscope.

[0058] Because the apparatus 82 shown in FIG. 4 is in the form of anendoscope, illumination would normally be required to be directed downthe endoscope, for example by optical fibre bundles (not shown). Therequired illumination may be fed in from the side of the apparatus 82. Acamera lead (not shown) may come in from the left of the apparatus 82.

[0059] Referring to FIG. 5, there is shown how polarising filters may beomitted from the display screen by using a lenticular overlay. Thelenticular overlay is used to cover a matrix of optical fibres where thelight emerges. This is to enable stereoscopic viewing by means ofangular separation of images, without the use of spectacles.

[0060] In order to exploit the lenticular overlay, vertical strips ofeach image alternate across the fibre optic matrix. The same arrangementmay be used for use with polarising spectacles which do not provide thesame restrictions on viewing position, but in this case light has to bepolarised for the images in opposite senses. Polarisation filters may beapplied either to the face of the display screen or in alternatelyopposite senses to columns of the fibres at the light output end. Thefirst, last and an intermediate fibre are illustrated in example columnsin FIG. 5 For example, the first column of picture elements for theright eye image is adjacent to the first column of picture elements forthe left eye image.

[0061]FIG. 5 shows examples of optical fibre routing. Thus, for avertical strip down the left hand side of the right eye image, lightentering a fibre at RS1 emerges at RR1. Similarly, for the left eyeimage, light emerges immediately adjacent at LR1. Further across thepicture, light entering at RS5 emerges at RR5 adjacent to thecorresponding part of the left eye image LR5. This form of imagemanipulation has the advantage of acting in line with a screen whichdoes not have to be displaced from its monoscopic viewing position.

[0062]FIG. 6 shows self-explanatory views of a television displaythrough polarising spectacles or a lenticular overlay. The verticalstrips at the bottom represent reassembled picture elements where there-orientation of the images has been implemented in the manner of FIG.5.

[0063] Referring now to FIGS. 7 and 8, there is shown apparatus 84 forthe optical manipulation of a pair of landscape stereoscopic images. Theapparatus 84 comprises a viewing window 86 covered by anti-reflectioncoated glass or plastic. In other respects the construction is acomponent part of FIG. 2 where the viewing face anti-reflection coatedglass or plastic comes later, and the image source may differ. Anenclosure 88 is preferably matt black on its inside. A filter 28 isprovided for circular polarisation, a filter 92 is provided for linearpolarisation, and a filter 30 is also provided for linear polarisation.The filter 30 may be omitted if desired but its presence helps tobalance brightness.

[0064] A liquid crystal thin film transistor panel 96 displays a mirrorimage of the left eye picture. A liquid crystal thin film transistorpanel 98 displays a mirror image of the right eye picture. The panelsare linked in the manner of a “video wall” to form a single screenhaving two halves. A conventional monoscopic video picture applied tothe combination would be displayed with half of its area on each panel.

[0065] A mirror 12 transmits and reflects light equally when at 45%.

[0066] Polarising spectacles 16 are employed as shown. The arrangementof panel polarisation and polarising filters is such that thepolarisation of each image is mutually exclusive. Each eye can only seethe appropriate picture.

[0067] A hinge 32 is employed for precise setting of the angle of themirror 8 for vertical alignment of the two images. An alternative methodwould be to slide the panel 98 forwards or backwards horizontally, asseen through the viewing window 86.

[0068] In a further modification of the apparatus 84, the panels 96, 98may be a single large panel.

[0069] It is to be appreciated that the embodiments of the inventiondescribed above with reference to the accompanying drawings have beengiven by way of example only and that modifications may be effected.Thus, for example, the apparatus 82 in the form of the endoscope shownin FIG. 4 could operate in an inverted manner in which the right eyechannel would be the straight channel.

1. Apparatus for the optical manipulation of a pair of landscapestereoscopic images, which apparatus comprises a housing, and opticalre-orientation means positioned in the housing and for re-orientatingthe pair of landscape stereoscopic images between a first orientationrequired for human viewing and a second orientation required forrecording with a single camera or for reproduction from a single screen,the single screen being such that it has a first pair of sides which areshorter than a second pair of sides, the second orientation being suchthat there is no top to bottom inversion of one of the landscapestereoscopic images with respect to the other one of the landscapestereoscopic images, the second orientation being such that thestereoscopic landscape images are rotated for display in each of twohalves of the single screen such that the longest sides of thestereoscopic landscape images are parallel with the first pair of sidesof the screen thereby maintaining a good aspect ratio without the needfor compression or stretching of the pair of landscape stereoscopicimages, and the optical re-orientation means being such that the pair oflandscape stereoscopic images leave the optical re-orientation means ina direction which is parallel to a direction in which the pair oflandscape stereoscopic images enter the optical re-orientation means. 2.Apparatus according to claim 1 and including a first optical path forconveying a first one of the pair of landscape stereoscopic images, anda second optical path for conveying a second one of the pair oflandscape stereoscopic images.
 3. Apparatus according to claim 2 inwhich the optical re-orientation means re-orientates one of the pair oflandscape stereoscopic images such that the landscape stereoscopicimages are side by side in landscape format at a first end of the firstand the second optical paths, such that the landscape stereoscopicimages are on top of one another at a second end of the first and thesecond optical paths, and such that the landscape stereoscopic imagesare the same way up at the first and the second ends of the first andthe second optical paths.
 4. Apparatus according to any one of thepreceding claims in which the optical re-orientation means comprisesfour reflective surfaces off which at least one of the landscapestereoscopic images is sequentially reflected.
 5. Apparatus according toany one of the preceding claims in which the optical re-orientationmeans comprises a coherent bundle of optical fibres in one or bothoptical paths.
 6. Apparatus according to claims 3 and 4 in which theoptical re-orientation means comprises a first one of the reflectivesurfaces for reflecting one of the landscape stereoscopic imagesupwardly, a second one of the reflective surfaces for reflecting theimage from the first reflective surface towards the second end of thefirst and the second optical paths, a third reflective surface forreflecting the image from the second reflective surface towards andabove the one of the landscape stereoscopic images that has not beenre-orientated, and a fourth reflective surface for reflecting the imagefrom the third reflective surface towards the second end of the firstand the second optical paths and parallel with and above the one of thelandscape stereoscopic images that has not been re-orientated. 7.Apparatus according to claim 4 or claim 6 in which the four reflectivesurfaces are four prism surfaces.
 8. Apparatus according to any one ofclaims 1-3 in which the optical re-orientation means includes threereflective surfaces off which at least one of the landscapedstereoscopic images is sequentially reflected, and electricalimage-reversal means for providing a screen output as a mirror image. 9.Apparatus according to claim 8 and including flat panel display means,and in which the stereoscopic pair of images from a flat panel displayon the flat panel display means are able to be superimposed andsegregated by passive polarising spectacles, despite the display panelhaving inbuilt polarisation opposite to that required for one of the twoimages.
 10. Apparatus according to any one of the preceding claims andwhich is in the form of an endoscope.